The Trump administration is adding hurdles and increasing scrutiny in the employment-visa application process, making it harder for businesses to hire foreign workers, and companies and immigration attorneys are bracing for more changes soon.

President Donald Trump has long campaigned against illegal immigration, but he also backs reductions to legal immigration, arguing that foreigners provide unneeded competition for Americans. So far, the administration hasn’t enacted wholesale policy changes to the employment-visa programs. Congress hasn’t enacted any new limits or changes either. But the administration has tightened the system in ways that together are making it tougher to import foreign workers.

The administration is more closely scrutinizing applications for the high-skilled visa program known as H-1B, sending back more than one in four applications between January and August via “requests for further evidence,” according to data from U.S. Citizenship and Immigration Services, known as USCIS, which administers the program. A year earlier, fewer than one in five were sent back.

The H-1B visas are heavily used by technology companies, including outsourcing firms. Businesses argue they need the visas to fill critical jobs while critics say they displace American workers.

H-1B applications for positions at the lowest pay level are getting particular scrutiny, with the government questioning whether the foreigner holds required specialized skills, according to several immigration attorneys. A directive from the agency specifically questions whether a computer programmer is a specialty occupation that qualifies for the visa. Many of these applications are being denied, attorneys say.

“The goal of the administration seems to be to grind the process to a halt or slow it down so much that they achieve a reduction in legal immigration through implementation rather than legislation,” said Ben Johnson, executive director of the American Immigration Lawyers Association, which often takes pro-immigration stances.

R. Carter Langston, a spokesman for USCIS, said that his agency’s policies align with the administration’s priorities, including “tightening standards” to deter fraud and abuse.

“USCIS is focused on ensuring the integrity of the immigration system through deliberative and fair adjudications all while protecting the interest of US workers,” he said.

For some, the changes are a long overdue correction. “They do slow the system down but in a good way,” said Jessica Vaughn of the Center for Immigration Studies, an advocacy group that backs limits to legal immigration.

People on both sides of the issue are anticipating further restrictions soon, following the confirmation in October of Francis Cissna as director of USCIS. Mr Cissna has a reputation as a skeptic of employment visa programs. He declined a request for an interview.

Two big regulatory changes are looming that would undo actions by the Obama administration that eased the way for high-skilled foreign workers.

The first change allowed spouses of H-1B workers the right to work. That regulation is being challenged in court and the Trump administration is expected to eliminate the provision rather than defend it. “The real fight within the government is not whether to terminate the program, but how fast they should kill it,” said Lynden Melmed, an attorney with Berry Appleman & Leiden LLP, who is tracking the internal debate.

The second change affects the Optional Practical Training program, which allows foreign graduates from U.S. colleges in science and technology an extra two years of work authorization, giving them time to win an H-1B visa. The Trump administration could kill that benefit or reduce the two-year window, according to people familiar with the discussions.

Meanwhile, a series of more modest changes that have added scrutiny to visa processing include:

•USCIS directed last month that adjudicators no longer pay “deference” to past determinations for renewal applications. This means an applicant’s past approval won’t carry any weight if he or she applies for a renewal.

•The agency is conducting more applicant interviews, which critics say slows the system. The agency spokesman said this process will ramp up over several years and is needed to detect fraud and make accurate decisions.

•In the spring, the agency suspended premium processing, which allowed for fast-track consideration to those who paid an extra fee. This option wasn’t resumed until October, meaning many workers who qualified for a coveted H-1B visa had to wait months for a decision.

•State Department officials have been told to consider that Mr. Trump’s “Buy American, Hire American” executive order directs visa programs to “protect the interests of United States workers.” And the Foreign Affairs Manual now instructs officers to scrutinize applications of students to ensure they plan to return to their home countries. A State Department official said the official rules haven't changed but said a “comprehensive” review is under way.

Some employers who use the visa programs have seen a dramatic change, such as Avant Healthcare Professionals, which recruits foreign nurses and occupational therapists for work in the U.S.

This year, every application filed by the company for an H-1B visa was returned with a request for further evidence, compared with 20% last year, said Shari Dingle Costantini, the company’s chief executive officer. The company has received results for only three applications and in each case it was told the application would likely be rejected.

Ms Costantini said the immigration agency is asking her company to prove it has money in hand to pay every employee’s wages, even though her business model is to place the workers at hospitals and other companies that actually pay the wages.

“It’s frustrating for us,” she said. “We’ve got clients across the country that need nurses and they’re not getting these nurses.”

Foreign students hoping to stay in the U.S. have also been affected.

Helen Wang, a 23-year-old from China, applied for an H-1B visa after finishing college so she could work as a market-research analyst at a job-recruitment website. Ms. Wang, who lives in Chicago, recalls excitement last spring when her employer was awarded a visa for her, one of 85,000 available in the government’s annual lottery. Her application was processed for months and then, this fall, was rejected.

“USCIS questioned whether this position needs an H-1B or not,” she said. She had to leave her job and now plans to go back to school in the U.S. to earn a master’s degree and try again for a work visa after those studies. “I have to find another solution to keep my legal status in the United States.”